Among song sparrows, the most tuneful males often win over the females—but their vocal expertise may come at a cost. Biologists at Duke University counted up songs in male song sparrows’ repertoires and then tested the birds’ memories.

Every day for eight days the researchers hid a mealworm in one of several shallow wells, some of which had lids. The mealworms’ location remained the same, so the scientists could observe how deftly the sparrows remembered where to find their treat.

Over time all of the birds improved, but the males that sang the fewest songs learned the quickest, while the birds with more expansive repertoires struggled. Kendra Sewall, now at Virginia Polytechnic Institute and State University, explains that the difference could reflect a trade-off during mental development—the birds develop one ability or the other.

The finding also suggests that females may be able to detect a potential mate’s weaknesses in his songs. Although many pick males that sing lots of songs, Sewall notes that every male in their study found a mate. It’s possible, she says, that certain females are aware of the trade-off and prefer a partner with spatial smarts to pass on to their young.

This story ran as “Silly Love Songs” in the September-October 2013 issue.